Hydrogen sulfide (H2S), although generally known for its toxicity and characteristic odor, is now recognized as an important signaling molecule with diverse biological roles. The biological roles of H2S range from roles in angiogenesis to wound healing. In mammals, H2S production is derived primarily from three enzymes: cystathionine-γ-lyase (CSE), cystathionine-β-synthase (CBS), and 3-mercaptopyruvate sulfotransferase (3-MST). The expression of these enzymes in different tissues suggests a broad importance and significance of H2S in the cardiovascular, circulatory, respiratory, urinary, and nervous systems. Abnormal H2S regulation, however, has been associated with hypertension, diabetes, as well as various diseases of mental deficiency including Down's syndrome and Alzheimer's disease. In addition to the pathophysiological conditions associated with H2S misregulation, H2S can also act on specific cellular targets, including heme proteins, cysteine residues on KATP channels, nitric oxide, and other emerging targets. As such, H2S-reactive compounds, compositions, kits, and methods of using the same are needed.